Meters installed in buildings for industrial or domestic use measure a quantity of energy (electricity) or of fluid (water, gas) consumed; some meters are suitable for storing data relating to consumption in a memory, e.g. in accumulated form by means of a totalizer having wheels. This data is used by the operating organization to bill the consumer. To obtain the data, it is common practice to read each meter visually. In order to reduce personnel costs and the time taken by such operations, proposals have been made, in known manner, to read meters remotely by means of "remote reading" or "remote relaying" systems comprising centralized collection means connected to each meter by a network of wire connections and suitable for collecting and storing data from each of the meters, generally on a periodic basis. The output from the collection means is connected to processing and/or communication means.
In addition to the advantages mentioned above compared with visual meter reading, remote reading or remote relaying firstly provides better safety by monitoring meters on a quasi-continuous basis, and secondly provides better management of user consumption.
Such systems are already known, as applies in particular to water meters.
A first family of known systems makes use of an existing communications network.
In a first example (CMR), the system uses a coaxial television cable connecting a central transmitter to a plurality of buildings (each containing one or more meters). The centralized collection means are connected to said cable. Each meter is connected to the cable via a device suitable for interrogating the corresponding meter. Interrogation and data transmission are performed in a random sequence imposed by said interrogation device.
In a second example, the system uses a telephone network connecting buildings containing meters to a telephone exchange itself connected by telephone line to premises belonging to the organization that distributes energy, water, or gas, and where the collection means are situated. Each meter is connected to an interrogation device which is normally in a standby state. The connection means control the exchange to actuate the interrogation device which, once "woken up", interrogates the meter and transmits the data to the exchange which in turn transmits the data to the collection means.
In a third known example, each meter is connected to a memory, itself connected to means for telephone communication via a modem which is connected to the telephone network.
Although these prior systems are satisfactory from certain points of view such as security and reliability, they nevertheless suffer from drawbacks.
A system in accordance with the first example requires an electrical power supply for the interrogation device. The system of the third example is expensive given that each meter has its own modem and its own telephone number.
In addition, systems in accordance with the first, second, and third above examples all make use of interrogation devices that are relatively expensive, and since they rely on an existing communications network, they can firstly only be installed in areas that are already provided with such networks, and secondly special precautions need to be taken to avoid interference between transmitting meter data and the original function of the network.
A second family of systems is also known which are provided with their own communication means.
A first known type of system (AKUDOM) comprises centralized collection means connected by a star network to each of the meters. The meters are of the "pulse emitting" type and are suitable for delivering a signal comprising one pulse per unit volume of water flow.
Although relatively cheap and of satisfactory reliability (the data from each meter is correctly identified), this prior system suffers from the drawbacks of requiring individual connections to each meter, and of being suitable for a limited range of applications only, given limitations firstly on the number of meters that can be connected in the system and secondly on the distance that may exist between each meter and the collection means.
A second type of known system (MAYA) includes central collection means connected by a common connection to a series of primary collection devices, each of which is connected to a plurality of "pulse-emitting" meters. On instructions from the central collection means, each primary collection device sequentially interrogates each of its meters.
This known system suffers from unacceptable drawbacks. The identity code for each meter is located in its primary collection device, and this is inconvenient both with respect to reliability and with respect to flexibility (when changing meters). In addition, having a primary collection device sharing a plurality of meters implies that the meters are distant therefrom and consequently increases the cost and the complexity of cabling.
Furthermore, the first and second types of system mentioned above both suffer from a defect specific to pulse-emitting meters, namely that they allow only relative encoding of the quantity of water consumed.
From U.S. Pat. No. 3,445,813 and from French patent application FR-A-2 582 894 a system is also known for remote transfer and collection of data, the system comprising a central unit and a plurality of addressable satellite units connected to one another via a common line, and in which data transmitted by a satellite unit to the central unit may include, in particular, the address of the satellite unit. However, such a system suffers from a lack of flexibility in operation, particularly with respect to updating the central unit with information about the satellite units.
In conclusion, it will be understood that a need is felt for a remote meter reading system which is simultaneously cheap to manufacture, to install, and to operate, reliable (both with respect to data transmission and with respect to data origin), flexible in use (making it simple to change a meter and to add and/or remove meters on the communication network), and which does not rely on an existing communication network.